HWN Suggests

Blood Gases: ABG vs. VBG

Hypoxemic patients, those with ARDS, and patients with poor circulation that prohibits plethysmography by pulse oximeter should have an ABG, because a VBG cannot be used to determine oxygenation. In such patients, this means you can start with an ABG and then correlate your end tidal CO2 and oxygenation with pulse oximetry (if oximetry then improves). If you are concerned about the patient’s metabolic acid-base status, a VBG will give you a pH, HCO3, lactate and BD that closely approximates the ABG. A venous pCO2 <45 mmHg will reliably screen for hypercarbia on a VBG, but the actual value may vary from that of an ABG with an average difference ranging from 5.7- 8.6mmHg.

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 ABG Interpretation

Arterial blood gas (ABG) interpretation is something that can be difficult to grasp initially (we’ve been there). We’ve created this guide, which aims to provide a structured approach to ABG interpretation whilst also increasing your understanding of each result’s relevance. The real value of an ABG comes from its ability to provide a near-immediate reflection of the physiology of your patient, allowing you to recognise and treat pathology more rapidly.

 ABGs vs. VBGs

ABGs are easy. Why not just do the ABG? It’s true that obtaining an arterial blood sample for ABG assessment is easy . . . for the physician. Unfortunately, they are quite painful for the patient.

 HOT TAKE - ABGs

Every time I’m asked to get an arterial blood gas (ABG) for a consultant or attending, I shudder. Well, I stop and think, and then 9 times out of 10, I shudder.

 Reading the ABG

The ABG is one of the most basic tests we run in the Emergency Department. It may be an ABG or a VBG. Regardless, it is an opportunity to gain information quickly.

Articles of Interest

A Review of Venous and Arterial Blood Gases in Emergency Medicine

Interpret the ABG in the ‘clinical context’ of the patient in front of you.

Arterial Blood Gas (ABG) Sampling

Precooling proved to be useful for patients who had problems with anxiety and pain due to arterial blood puncturing. Cryoanalgesia can be provided by ice bag applied to wrist 3 minutes prior to arterial puncture.

Blood-Gas Analysis and the Emergency Patient: a Review

Normally, Paco2 ranges from 35 mm Hg to 45 mm Hg. A PaCO2 value below 35 mm Hg reflects hyperventilation or increased carbon dioxide elimination; a value above 45 mm Hg indicates hypoventilation or decreased carbon dioxide elimination. Tachypnea may or may not result in a lower PaCO2 value. People with asthma, for example, may have a respiratory rate of 30 but half the usual tidal volume, so the PaCO2 will stay within the normal range.

Can VBG analysis replace ABG analysis in emergency care?

Arteriovenous agreement for pH is such that values are clinically interchangeable and agreement for bicarbonate is also close. Agreement for pCO2 is poor with 95% limits of agreement of the order of 20 mm Hg (2.67 kPa); however, there is solid evidence that a venous pCO2 ≤45 mm Hg (6 kPa) reliably excludes clinically significant hypercarbia. Evidence regarding arteriovenous agreement for base excess is unclear. Given knowledge of the performance characteristics of VBG analyses, integration of the clinical findings with VBG results is often sufficient to safely guide treatment decision making.

Mastering Your ABGs

You can analyze the ABGs using the ROME method. ROME stands for Respiratory Opposite Metabolic Equal. How does it work? You think of respiratory when one is high and the other one is low. You think of metabolic when ABGs are on equal values.

POTD: ABG vs VBG

When should you order an ABG and when does a VBG suffice?

The Pitfalls of Arterial Blood Gases

It is great to be able to determine the acid-base balance and oxygenation status. However, being able to correlate these to the patient—to determine if normalization is good or bad, or to know if the time for concern has passed or just gotten more critical—is the real key to making effective interpretation and use of the arterial blood gas test.

The VEINART Trial: VBG vs ABG

Venous blood gas is less painful for patients than ABG in non-hypoxaemic patients. Venous blood gas should replace ABG in this setting.

VBG versus ABG

In general, ABGs rarely need to be performed unless an arterial line is in place (for arterial blood pressure monitoring and ease of blood sampling)

VBG vs ABG in the ED

Increasing data shows that for most clinical indications, data from VBG correlates well, and are just as useful as that from ABG.

What's in a Blood Gas? VBG vs ABG

e. You send VBGs as part of the work up for all these patients finding hypercarbia for the patients who have COPD exacerbations and a significant metabolic acidosis in the patient with T1DM confirming your diagnosis of DKA. You are in the process of admitting these patients when you face questions from your colleagues in-house as to why you didn’t perform an ABG on these patients?